I can not add more user even we have enough license

I can not add more user even we have enough license

Hi,

we are new to ZOHO. we buy 17 standard license and 13 user added till now, but for 14th user creation I get 
" Max user license limit reached. Please purchase/upgrade license to add more user(s) with mailboxes."

I tried to add p.jafari@youbgroup.com.

please help and let me know the results.
regards